Dispatching and scheduling memory operations in an electronic printing system

Abstract: A method for scheduling transfers in a printing machine (Fig. 2) of the type having a scheduler (162;Fig. 9) communicating with both a first disk (Disk 0) and a second disk (Disk 1), the first and second disks having a combined bandwidth. The method for scheduling comprises the following steps: First, a first transfer (CurrentO p 1) to be performed on a first location of the first disk (Disk 0) during a first time interval (t SX1 -t DX1 ) and a second transfer (NextO p 1) to be performed on a second location of the first disk (Disk 0) during a second time interval (t SX2 -t DX2 ) are both scheduled, with the scheduler (162), so that a first time gap interval (t GAPx ) exists between the first time interval (t SX1 -t DX1 ) and the second time interval (t SX2 -t DX2 ) . Second, a third transfer (CurrentO p 2) to be performed on a first location of the second disk (Disk 1) during a third time interval (t SY1 -t DY1 ) and a fourth transfer (NextO p 2) to be performed on a second location of the second disk (Disk 1) during a fourth time interval (t SY2 -t DY2 ) are both scheduled, with the scheduler (162), so that a second time gap interval (t GAPy ) exists between the third time interval (t SY1 -t DY1 ) and the fourth time interval (t SY2 -t DY2 ) . Finally, a fifth transfer (InsertO p ) to be performed during a fifth interval (t SI -t DI ) is scheduled, with the scheduler (162), so that the fifth interval (t SI -t DI ) occurs during either the first time gap interval (t GAPx ) or the second time gap interval (t GAPy ) in a manner that maximizes the combined bandwidth of the first (Disk 0) and second (Disk 1) disk.

Description: The present invention relates generally to resource management of a memory arrangement in an electronic printing system and, more specifically, to a technique for dispatching and scheduling transfers in the memory arrangement. In an electronic printer, of the type known is DocuTech® and manufactured by Xerox® Corporation, various components ("clients"), such as a marking engine, are linked to a main memory by way of a system memory. In the preferred embodiment the main memory preferably comprises a plurality of hard disks. The use of a plurality of hard disks to store redundant files is disclosed in US-A-5,155,845. For the above-mentioned electronic printer, files are transferred between the clients and the main memory through use of a resource manager, which resource manager schedules access to the disks for the clients. The data to be transferred to the disks is held in the system memory, the system memory being managed as a chain of buffers by the resource manager. To achieve such management, buffers assigned to specific clients are handed to the resource manager and then written to the main memory whenever bandwidth is available. Since each seek of the disks incurs a seek overhead, the number of seeks is minimized by chaining buffers together and tranferring the chained buffers between a client and one of the disks in a single operation. For example, resource manager can link together buffers that are to be written to contiguous locations on one or more disks, the writting being responsive to attaining a preset threshold. Further information regarding an implementation of resource management can be obtained by reference to US-A-5,142,667. In the DocuTech® system, files are preferably stored in one of two configurations: "replicated" files which have a copy on each disk, and "superdisk" files, segments of which are "striped" across each disk. In a multi-function system with one or more disks, such as DocuTech®, throughput becomes a "bottleneck" resulting in skipped pitches, and thus delays in printing. In a "print shop" environment, such delays are unacceptable. For disk I/O a replicated file transfer is 1/N times that of a superdisk file transfer rate, where N is equal to the the number of disks in the superdisk. That is, when a client requests a read of a replicated file only one disk is involved in the resulting data transfer and (N-1)/N of the available disk bandwidth is not utilized. In the print shop environment it is essential that maximum disk utilization be achieved so that disk bandwidth is maximized Accordingly transfer operations should be performed for all of disks, in parallel, on an on-going basis. Moreover, while US-A-5,142,667 discloses a desirable scheduling approach for a resource management scheme, such approach does not necessarily insure that a plurality of disks will be kept as busy as possible or that combined bandwidth will be maximized. It would be desirable to provide a process which optimzes transfers of files between various clients and a plurality of disks so that the combined bandwidth of the plurality of the disks is maximized. In accordance with the present invention there is provided a method for scheduling transfers in a printing machine of the type having a scheduler communicating with both a first disk and a second disk, the first and second disks having a combined bandwidth, comprising the steps of: a) scheduling, with the scheduler, a first transfer to be performed on a first location of the first disk during a first time interval and a second transfer to be performed on a second location of the first disk during a second time interval so that a first time gap interval exists between the first time interval and the second time interval; b) scheduling, with the scheduler, a third transfer to be performed on a first location of the second disk during a third time interval and a fourth transfer to be performed on a second location of the second disk during a fourth time interval so that a second time gap interval exists between the third time interval and the fourth time interval; and c) scheduling, with the scheduler, a fifth transfer to be performed during a fifth time interval, the fifth time interval occurring during a selected one of the first time gap interval and the second time gap interval in a manner that maximizes the combined bandwidth of the first and second disks. Preferably, step c) further includes the steps of obtaining a first sum time by summing the following 1) a first seek time required to move a first disk head along the first disk from the first location on the first disk to a fifth location associated with the fifth transfer, 2) the fifth time interval, and 3) a second seek time required to move the first disk head along the first disk from the fifth location to the second location on the first disk; and obtaining a second sum time by summing the following: 1) a third seek time required to move a second disk head along the second disk from the first location on the second disk to the fifth location, 2) the fifth time interval, and 3) a fourth seek time required to move the second disk head along the second disk from the fifth location to the second location on the second disk. Preferably, the sum times have respective magnitudes, and step c) is performed with the respective magnitudes. In accordance with yet another aspect of the present invention there is provided an apparatus for scheduling transfers in a printing machine, comprising: a) a first disk and a second disk, the first and second disks having a combined bandwidth; b) a scheduler coupled for communication with both the first and second disks; characterised in that the scheduler is adapted to (i) schedule a first transfer to be performed on a first location of the first disk during a first time interval and a second transfer to be performed on a second location of the first disk during a second time interval so that a first time gap interval exists between the first time interval and the second time interval; (ii) schedule a third transfer to be performed on a first location of the second disk during a third time interval and a fourth transfer to be performed on a second location of the second disk during a fourth time interval so that a second time gap interval exists between the third time interval and the fourth time interval; and (iii) schedule a fifth transfer to be performed during a fifth time interval, the fifth time interval occurring during a selected one of the first time gap interval and the second time gap interval in a manner that maximizes the combined bandwidth of the first and second disks. These aspects of the invention will become apparent from the following description, the description being used to illustrate a preferred embodiment of the invention when read in conjunction with the accompanying drawings. Figure 1 is a perspective view of an electronic printing system upon which a technique of the present invention can be executed; Figure 2 is a block diagram of the electronic printing system of Figure 1; Figure 3-5 conjunctively represent a block diagram of the controller section of Figure 2; Figure 6 is a block diagram depicting a technique for storing image files on the plurality of disk drive devices to provide super disk files; Figures 7 and 8 conjunctively represent a block diagram depicting a technique for collecting system files and replicating them; Figure 9 is a schematic, block diagram of resource manager operatively coupled with both a plurality of disk drive devices and a system memory, the system memory including a plurality of sets of parameters; Figure 10 is a schematic, enlarged view of one of the sets of parameters shown in Figure 9; Figures 11 and 12 conjunctively represent a flow diagram depicting the operation of a dispatcher of Figure 9; Figure 13 is a schematic representation of various transfers or operations as scheduled on the plurality of disk drive devices; and Figures 14 and 15 conjunctively represent a flow diagram for the operation of the scheduler of Figure 9. Referring to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and more particularly to Figures 1 and 2, there is shown an exemplary image printing system 2 for processing print jobs in accordance with the teachings of the present invention. Printing system 2 for purposes of explanation is divided into image input section 4, controller section 7, and printer section 8. In the example shown, image input section 4 has both remote and on-site image inputs, enabling system 2 to provide network, scan, and print services. Other system combinations may be envisioned such as a stand alone printing system with on-site image input (i.e., a scanner), controller, and printer; a network printing system with remote input, controller, and printer; etc. While a specific printing system is shown and described, the present invention may be used with other types of printing systems. For example, printer section 8 may instead use a different printer type such as ink jet, ionographic, thermal, photographic, etc., and furthermore may be incorporated in electronic display systems, such as CRTs, LCDs, LEDs, etc. or else other image scanning/processing/recording systems, or else other signal transmitting/receiving,recording systems, etc. as well. A more detailed description of printing system 2 may be found in US-A-5,057,869. Referring to Figure 2, controller section 7 is, for explanation purposes, divided into an image input controller 50, User Interface (UI) 52, system controller 54, disk memory 56, image manipulation section 58, Resource Manager 57, Diagnostic Manager 59, and image output controller 60. As best seen in Figure 1, UI 52 includes a combined operator controller/CRT display consisting of an interactive touchscreen 62, keyboard 64, and mouse 66. UI 52 interfaces the operator with printing system 2, enabling the operator to program print jobs and other instructions, to obtain system operating information, visual document facsimile display, programming information and icons, diagnostic information and pictorial views, etc. Items displayed on touchscreen 62 such as files and icons are actuated by either touching the displayed item on screen 62 with a finger or by using mouse 66 to point a cursor to the item selected and keying the mouse. Referring to Figures 2-5, the scanned image data input from scanner section 6 to controller section 7 is compressed by image compressor/processor 51 of image input controller 50 on PWB 70-3. The compressed image data with related image descriptors are placed in image files and temporarily stored in system memory 61 pending transfer to main memory 56 where the data is held pending use. A preferred procedure for storing image files is discussed below. When the compressed image data in memory 56 requires further processing, or is required for display on touchscreen 62 of UI 52, or is required by printer section 8, the data is accessed in memory 56 and transferred to system memory 61 (see Fig. 3). Where further processing other than that provided by processor of image input section 4 is required, the data is transferred to image manipulation section 58 on printed wiring board (PWB) 70-6 (see Fig. 5) where additional processing steps such as collation, make ready (document editing), decomposition, rotation, etc. are carried out. Following processing, the data may be returned to main memory 56, sent to UI 52 for display on touchscreen 62, or sent to image output controller 60. Resource Manager 57 controls access to disks and system memory (RAM) 61 of files while diagnostic manager 59 handles system faults. Image data output to image output controller 60 is decompressed and readied for printing and output to printer section 8. Image data sent to printer section 8 for printing is normally purged from memory 56 to make room for new image data. As shown in Figures 3-5, controller section 7 includes a plurality of PWBs 70 coupled with one another and with System Memory 61 by a pair of memory buses 72, 74. Memory controller 76 couples System Memory 61 with buses 72, 74. PWBs 70 include system processor PWB 70-1 having plural application or system processors 78; low speed I/O processor PWB 70-2 (Fig. 4) having UI communication controller 80 for transmitting data to and from UI 52, Boot Control & LSIO Services Processor 73, and Boot Bus Processor 75; PWBs 70-3, 70-4, 70-5 having disk drive controller/processors 82 with disk drives 83 for transmitting data to and from disks 90-1, 90-2, 90-3 respectively of main memory 56 (image compressor/processor 51 for compressing the image data and another application processor 78 are on PWB 70-3); image manipulation PWB 70-6 (Fig. 5) with image manipulation processors of image manipulation section 58; image generation processor PWBs 70-7, 70-8 with image generation processors 86 for processing the image data for printing by printer section 8; dispatch processor PWB 70-9 having dispatch processors 88, 89 for controlling transmission of data to and from printer section 8; and boot control-arbitration-scheduler PWB 70-10 having Channel Loader/Scheduler Processor 76, Boot Bus Processor 77, Boot Download Control Logic 79, and Memory Bus Arbitration Logic/Resource Manager 57. Loader/Scheduler Processor 76 has two functions, one as a Boot channel to bring the system to the ready state and the other as a scheduler channel used to decide which channel performs which task and in which sequence the tasks will be performed. Each independent processor and associated circuitry form a channel 81. Channels 81 (an example is shown in Figure 4) are independent processors for handling the applications software, or input/output processors for handling peripheral devices such as disk drives. For example, there are disk channels used to interface disk drives 83 for disks 90-1, 90-2, 90-3, scanner interface channel, printer interface channel, etc. Main memory 56 has plural hard disks 90-1, 90-2, 90-3 on which image files 140 and system files 142 are stored (Fig. 7). For ease of discussion, the disks 90-1, 90-2 and 90-3 may be referred to simply as "disks 90". System files comprise system operating files such as boot files 124, software files, data files 122, font-related files, etc., while image files are, in one example, files of scanned image data. System files are viewed as critical because of their importance to the operation of the system while image files are viewed as non-critical since these files may be recaptured by re-scanning the source document. System memory 61, which comprises a Random Access Memory or RAM, serves as a temporary store for data required during system operations. Memory 61 stores bits of data which can be written to (Data Entered) or read from (Data Used) the memory. Other data in memory 61 is used for reference and remains loaded as long as power is supplied. Since memory 61 is volatile, that is, all data is lost when power to memory 61 is terminated, Non Volatile Memory or NVM, which essentially comprise RAM memory with battery backup to supply DC voltage when power is turned off, are provided at several locations in the system as, for example, NVM 63 on Low Speed I/O Processor PWB 70-2 (Figure 4). NVM 63 is used to store file management updates and file content updates. EP-A-478,337, corresponding to U.S. Patent Application No. 07/590,634, entitled "Method of Operating Disk Drives in Parallel", a copy of which was filed with the present application, describes what will be referred to herein as Super Disk. Super Disk allows faster read/write access to files since all disks 90-1, 90-2, 90-3 can be accessed simultaneously. The risk incurred in this type of arrangement, however, is the loss of parts of a file should one or more of the disks fail which effectively results in loss of the entire file . Referring to Figure 6, to implement Super Disk, image files 140 to be transferred to disks 90-1, 90-2, 90-3 are divided by divider logic 143 into an even number of segments or sectors 144, each sector 144 being a preset number of bytes. The sectors are written in succession to successive disks until all of the sectors that comprise the image file are stored. Where N is equal to the number of disks, the total number of sectors 144 is an even multiple of N. In the example discussed, there are 3 disks 90-1, 90-2, 90-3 and therefore N = 3. Accordingly, image files are divided into a plurality of sectors 144 which are in effect grouped into blocks of 3 sectors each. That is, sector 1 of image file 140 is written to disk 90-1, sector 2 to disk 90-2, sector 3 to disk 90-3, sector 4 to disk 90-1, sector 5 to disk 90-2, and so forth and so on. As will be understood, where the number of bytes in a file is not evenly divisible into sectors 144, one or more of the sectors 144 in the last block may be empty or partially empty of data. As a result, one larger storage media or super disk is effectively formed. Image location logic 146 designates the location for each sector on disks 90-1, 90-2, 90-3, with the address of each corresponding block of sectors (.i.e., sectors 1, 2, 3; sectors 4, 5, 6, etc) being the same. Image data sequence logic 148 controls the disk writing sequence, while write/read control logic 150 provides the actual instructions to write or read image data to or from disks 90-1, 90-2, 90-3. Image data read from disks 90-1, 90-2, 90-3 is reconstructed by read control logic 152 which reads the image file sectors back from disks 90-1, 90-2, 90-3 in the same manner as the data was written to disks 90-1, 90-2, 90-3. Referring to Figures 7 and 8, system files 142 are normally permanent files which must be maintained. It should be recognized, however, that system files comprise other critical information, such as font-related information. To assure retention, system files 142 are replicated on each of the disks 90-1, 90-2, 90-3 at the same address. Replicated files are written simultaneously to all three disks 90-1, 90-2, 90-3, with the disk heads in the same position. System files 142, whether updates 120 of data files 122 that occur periodically during operation and life of the system 2 or new files such as new or upgraded software entered as software boot files 124, are written to one disk, as for example center disk 90-2, through Disk Drive Control Processor 82 for disk 90-2. The system files are thereafter migrated to the other disks, in this case, top and bottom disks 90-1, 90-3. Read control 154 reads system files 142 from any one of the disks 90-1, 90-2, 90-3. For additional explanation, reference is had to JP-1-4320518 (11.11.92), corresponding to U.S. Patent Application No. 07/678,925, entitled "A Process For Replacing storage Media In Electronic Printing Systems", filed April 1, 1991, a copy of which was filed with the present application. As a result, both Super Disk files (i.e., image files 140 with segments distributed equally across disks 90-1, 90-2, 90-3 of the system) and replicated files (i.e., duplicate system files 142 with copies on the disks 90-1, 90-2, 90-3) are created. When Super Disk files are accessed, all disks 90-1, 90-2, 90-3 are busy retrieving/storing data from/to disks. When a copy of a replicated file is accessed for reading, only one disk is busy. Referring to Figure 9, the relationship between the resource manager 57, system memory 61 and the disks 90 is shown in further detail. The resource manager 57, which is shown as operatively coupled with the system memory 61, includes a dispatcher 160 and a scheduler 162, whose operation will be discussed in further detail below. The various functions of the dispatcher and scheduler are performed with one or more processors. Preferably, the system memory includes a plurality of disk queues 164-167, each of which queue includes one or more sets of parameters. For ease of discussion below, the sets of parameters in the disk queue 164 are designated with the letters X 1 , Y 1 , Z 1 , I, X 2 , Y 2 and Z 2 , respectively. Each set of parameters, which is typically bundled and scheduled in time with one or two sets of parameters, corresponds to a file which is stored on one of the disks 90. In the preferred embodiment, the queue 164 designates files which are reserved for printing with a marking engine of the printer 8. The queue 165 designates files of clients having guaranteed bandwidth in the printing system 2, the queue 166 designates files of clients having nonguaranteed bandwidth in the printing system 2, and queue 167 designates files in cache. Any of the files in the queues can comprise a replicated file or a super disk file . Referring to Figure 10, exemplary parameters of one of the sets of parameters are shown. These exemplary parameters are derived from one of three sources. First, information regarding the general nature of the file, i. e. whether it is replicated or super disk, along with corresponding start and end points on the disk(s) (i. e. "start cylinder" and "end cylinder"), is provided by use of a volume allocation table ("VAT"). Details regarding the implemention and operation of a preferred VAT is described in US-A-5,212,786, entitled "File Compaction Process for Electronic Printing System". Second, information regarding "start time" of a file transfer is supplied from one of the clients. Finally, since the resource manager 57 retains pertinent information regarding files stored on the disks and has access, from the clients, regarding the number of disk pages occupied by the file, it can calculate time intervals, such as the "seek time" associated with moving a disk head to a location on the disk at which the data of the file is disposed and the end time of the file transfer. Moreover, with information regarding the general nature of the file and the number of disk pages occupied by the file, the interval of the "tranfer time" for the file can be determined readily. Referring to Figures 9 and 11-12, the operation of the dispatcher 160 is described in further detail. At step 200, the dispatcher 160 determines "available" disk(s) and, at step 202, it searches the disk queues (164-167). Upon selecting a candidate operation from the queue, i. e. "DiskOp" (step 204), one or more "possible" disks upon which the DiskOp can be performed are determined, at step 206, by reference to a suitable VAT. Preferably, such suitable VAT is implemented in accordance with the description of US-A-5,212,786. At step 208, it is determined whether the the possible disks are null. That is, it is determined whether the disk or disks upon which the DiskOp can be performed are in some way faulty. If the possible disk(s) is null then a disk fault indication is provided at step 210; otherwise, the process proceeds. If the DiskOp is a replicated operation ("ReplicatedOp") (step 212), then it is determined, via step 214, whether the ReplicatedOp is a read operation or a write operation. Provided the ReplicatedOp is a read operation, then, via step 216, a possible disk(s) is assigned to a disk(s) which is both "possible and available". Assuming that the possible disk assigned in step 216 is not null (step 220), then the possible disk is assigned to a "select" disk (step 222), the bandwidth required for the operation is calculated from the corresponding set of parameters in the queue (step 224), if necessary, and the read operation for ReplicatedOp is returned for the select disk (step 226). Referring again to step 214, if the ReplicatedOp is a write operation, then it is determined, at step 228, whether a file can be written to each of the three disks. When the possible disks are not equal to the available disks (step 228), then the process retrurns to step 202 and selects another candidate "DiskOp" at step 204. When, on the other hand, the possible disks are equal to the available disks, then the process continues through step 220, to determine if any of the disks are null, and through steps 222, 224 and 226, to perform write operations on each of the three disks. Referring again to step 212, if candidate DiskOp does not equal ReplicatedOp, then it is determined, at step 230, whether available disk(s) equals super disk. Provided available disk(s) does not equal super disk, then the process returns to step 202 and selects another candidate "DiskOp" at step 204. When available disk(s) equals super disk, then the process continues through step 220, to determine if any of the disks are null, and through steps 222, 224 and 226, to perform a designated Super Disk operation, i. e. to read or write preselected segments of information from each of the disks. Referring to Figures 9 and 13-15, the operation of the scheduler 162 is discussed in further detail. Referring specifically to Figures 9 and 13, the scheduling of the transfers designated in queue 164 as X 1 , Y 1 and Z 1 are scheduled across disks 90-1 (disk 0), 90-2 (disk 1) and 90-3 (disk 2) as "CurrentOp1", CurrentOp2" and "CurrentOp3". That is, transfer "X 1 ", having respective start and end times of "t SX1 " and "t DX1 ", is scheduled on disk 0, transfer "Y 1 ", having respective start and end times of "t SY1 " and "t DY1 ", is scheduled on disk 1 and transfer "Z 1 ", having respective start and end times of "t SZ1 " and "t DZ1 " is scheduled on disk 2. Subsequently, three more transfers, namely X 2 , Y 2 and Z 2 are scheduled on disks 0,1 and 2, respectively. As illustrated in Figure 13, the time intervals for the transfers X 2 , Y 2 and Z 2 are designated as "NextOp1", "NextOp2" and "NextOp3", respectively. Design of the printing system 2 dictates that each CurrentOp be spaced, in time, from the corresponding "NextOp". This spacing, however, tends to reduce the combined bandwidth of the disks 90. It has been found that bandwidth can be maximized by inserting a transfer, namely an "InsertOp" (designated by the letter "I" in queue 164 of Figure 9), between a given set of CurrentOp and NextOp. By maximizing the combined bandwidth of the disks, clients of the printing system 2 are better served and operation of the printing system 2 is optimized. Before proceeding to the optimization scheme of Figures 14 and 15, a few comments regarding Figure 13 are in order. When InsertOp is scheduled between CurrentOp and NextOp, an initial seek time is required to move a disk head from the location at which the CurrentOp is ended and the InsertOp is started. Additionally, a final seek time is required to move the disk head from the location at which the InsertOp is ended and the NextOp is started. It has also been found that, in one example, even when InsertOp can be performed on any one of the three disks, as shown in Figure 13, bandwidth is maximized when InsertOp is scheduled on a particular one of the disks. As will appear, inserting InsertOp to maximize bandwidth is not necessarily a straightforward process. In particular, referring still to the example of Figure 13, scheduling InsertOp on the disk in which CurrentOp has the shortest time interval, namely disk 2, does not necessarily result in an earliest end time, i. e. an "EET". Moreover, scheduling InsertOp on the disk in which the combined seek time (initial seek + final seek time) has the shortest time interval, namely disk 1, does not necessarily result in the EET. Indeed, it may be that neither the disk with the shortest CurrentOp time interval, namely disk 2, nor the disk with the shortest combined seek time interval, namely disk 1, possesses the EET. Without some sort of suitable software to determine EET, it would not necessarily be apparent that, in the example of Figure 13, disk 0 actually possesses the EET. Referring to Figures 9 and 14-15, the optimization scheme or technique for determining EET is described in further detail. The example of Figures 14-15 is intended to apply specifically to at least three types of insertions. First a replicated read operation can be inserted among other replicated read operations. Second, a Super Disk read operation can be inserted among other superdisk read operations. Finally, a Super Disk write operation can be inserted among other Super Disk write operations. It will be appreciated by those skilled in the art, however, that various other types of insertions are contemplated by the present technique. It should also be appreciated that the present technique is based on two simplifying assumptions, the assumptions being helpful, but not essential for the successful implementation of the technique. First, a Super Disk operation occurs on all three disks simultaneously. Second, the operations are sorted in the queue 164 so that Super Disk operations, which tend to comprise image files, are performed prior to replicated operations. At step 230 (Figure 14), a starting point is found in the queue 164, and, at step 232, a target disk(s) is determined. Throughout the present discussion of Figures 14-15, certain steps will be discussed in the context of inserting a replicated operation between two replicated operations on a single disk and other steps will be discussed in the context of inserting a Super Disk operation between two Super Disk operations, i. e. inserting three segments across three disks, respectively. It will be appreciated by those skilled in the art that the flow diagram of Figures 14-15 is applicacable, as a minimum, to both contexts. Using the target disk, NextOp is found. At step 236, a gap time interval between CurrentOp and NextOp ("t GAP ") is calculated, and, at step 238, t GAP is compared with the time interval of InsertOp ("t I "). If t GAP is less than t I , then the process proceeds to step 256, the significance of which step will be discussed in further detail below. Provided that t GAP is greater than or equal to t I , then the total seek time("t INITIAL SEEK + t FINAL SEEK ")(t TOTAL SEEK ) is calculated at step 248. If t GAP is less than the sum of both t I and t TOTAL SEEK ("t SUM "), as determined at step 250, then the process proceeds to step 256 When, however, the gap is greater than or equal to t SUM , then t SUM is, via step 252, compared to the current value of EET In the preferred embodiment, EET is initialized at a relatively high, arbitrary value. Hence for an initial pass through the the flow diagram of Figures 14-15, the process proceeds to step 254. For subsequent passes, if t SUM is less than EET, then the process proceeds to step 256. Provided that t SUM is greater than or equal to the current value of EET, then EET assumes the current value of t SUM and an insert point for InsertOp is set at the end of CurrentOp. At step 256, it is determined whether InsertOp is a replicated operation or a Super Disk operation. If InsertOp is a Super Disk operation, then it is presumed that three transfers are scheduled on the disks 0, 1 and 2, respectively, and another operation is fetched, via step 258, from the queue 164. Provided, that InsertOp is a replicated operation, then it is determined, at step 260, whether the CurrentOp is a replicated operation or a Super Disk operation. If the CurrentOp is a replicated operation then the process proceeds to step 258. If, on the other hand, the CurrentOp is a Super Disk operation, then step 262 is used to insure that each of the disks 0, 1 and 2 have been considered appropriately. That is the process does not proceed to step 258 until the target disk assumes the value of the "last" disk. In any event, the process proceeds to step 266, where CurrentOp is assigned the value of NextOp, and then to step 268 where the disk(s) is examined to determine if CurrentOp is null. If CurrentOp is null, then the process proceeds to EXIT, and if CurrentOp is not null then the moment at which CurrentOp begins is checked at step 270. When CurrentOp starts after EET, the process proceeds to EXIT; otherwise the process loops back to step 232 and continues until the optimum EET is found. Numerous advantages of the present invention will be appreciated by those skilled in the art. One advantage of the present invention is that operations can be scheduled in a manner which maximizes combined bandwidth of a plurality of disk drive devices. The printing of files is facilitated by maximizing the combined bandwidth, and service to clients having nonguaranteed bandwidth is optimized. Another advantage of the present invention is that the plurality of disk drive devices is kept as busy as possible. That is operations are dispatched continuously to respective disk drive devices unless all of the disk drive devices are busy or a group of operations cannot be performed because a plurality of the disk drive devices is not available. Yet another advantage of the present invention is that flexible scheduling and dispatching techniques, which are suitable for use with both replicated and super disk files, are provided. For example, in accordance with these techniques, a plurality of operations can be dispatched to or scheduled on a plurality of disk drive devices simultaneously.

Claims: A method for scheduling transfers in a printing machine (2) of the type having a scheduler (162) communicating with both a first disk (90-1) and a second disk (90-2) the first and second disks having a combined bandwidth comprising the steps of: a) scheduling, with the scheduler (162), a first transfer (X 1 ) to be performed on a first location of the first disk (90-1) during a first time interval (t SX1... t DX1 ) and a second transfer (X 2 ) to be performed on a second location of the first disk during a second time interval (t SX2... t DX2 ) so that a first time gap interval (t DX1... t SX2 ) exists between the first time interval and the second time interval; b) scheduling, with the scheduler (162), a third transfer (Y 1 ) to be performed on a first location of the second disk (90-2) during a third time interval (t SY1... t DY1 ) and a fourth transfer (Y 2 ) to be performed on a second location of the second disk during a fourth time interval (t SY2... t DY2 ) so that a second time gap interval (t DY2... t SY2 ) exists between the third time interval and the fourth time interval; and c) scheduling, with the scheduler (162), a fifth transfer (I) to be performed during a fifth time interval (t SI... t DI ), the fifth time interval occurring during a selected one of the first time gap interval (t DX1... t SX2 ) and the second time gap interval (t DY1... t SY2 ) in a manner that maximises the combined bandwidth of the first and second disk (90-1, 90-2). The method of claim 1, wherein the transfers (X 1 , X 2 , Y 1 , Y 2 ) are designated by sets of parameters, the method comprising: storing the sets of parameters; wherein the scheduling of transfers in steps (a) to (c) is dependent upon the sets of parameters. The method of claim 2, wherein the sets of parameters are ordered in a queue (164...167). The method of claim 3 in which each set represents a selected one of a first file type and a second file type, wherein said queue is sorted so that transfers associated with sets of the first file type are performed substantially prior to transfers associated with sets of the second file type. The method of any of claims 2 to 4, in which the sets of parameters are ordered in a plurality of queues (164...167), further comprising means for searching said queues to dispatch a transfer to a selected one of said plurality of disk drive devices (83). The method of claim 5, in which a transfer is being performed currently on each of said plurality of disk drive devices (83), wherein the dispatched transfer is transferred to the selected one of said plurality of disk drive devices as soon as the transfer being performed thereon is completed. The method of any of the preceding claims, wherein said image input terminal comprises a scanning device for generating the image data of the plurality of image files, the machine preferably further comprising a printing device, communicating with said plurality of disk drive devices (83), for printing image data associated with a selected one of the image files. An apparatus for scheduling transfers in a printing machine (2), comprising: a) a first disk (90-1) and a second disk (90-2), the first and second disks having a combined bandwidth; b) a scheduler (162) coupled for communication with both the first and second disks; characterised in that the scheduler is adapted to (i) schedule a first transfer (X 1 ) to be performed on a first location of the first disk (90-1) during a first time interval (t SX1... t DX1 ) and a second transfer (X 2 ) to be performed on a second location of the first disk during a second time interval (t SX2... t DX2 ) so that a first time gap interval (t DX1... t SX2 ) exists between the first time interval and the second time interval; (ii) schedule a third transfer (Y 1 ) to be performed on a first location of the second disk (90-2) during a third time interval (t SY1... t DY1 ) and a fourth transfer (Y 2 ) to be performed on a second location of the second disk during a fourth time interval (t SY2... t DY2 ) so that a second time gap interval (t DY1... t SY2 ) exists between the third time interval and the fourth time interval; and (iii) schedule a fifth transfer (I) to be performed during a fifth time interval (t SI... t DI ), the fifth time interval occurring during a selected one of the first time gap interval (t DX1... t SX2 ) and the second time gap interval (t DY1... t SY2 ) in a manner that maximises the combined bandwidth of the first and second disk (90-1, 90-2). The apparatus of claim 8, further including a resource manager (57) suitably programmed for carrying out the method of any of claims 2 to 7.

Inventors: COMPARETTA CHRISTOPHER, ENZIEN COLLEEN R, FEDERICO ANTHONY M, IPPOLITO RONALD A, LEGG ERNEST, MAY KEITH A, SATHI KITTY, STEGBAUER RANDALL J, COMPARETTA, CHRISTOPHER, ENZIEN, COLLEEN R., FEDERICO, ANTHONY M., IPPOLITO, RONALD A., LEGG, ERNEST, MAY, KEITH A., SATHI, KITTY, STEGBAUER, RANDALL J.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1994
Main classification: G03G15
IPC codes: G06F3, H04N1, G06K15